Note: Descriptions are shown in the official language in which they were submitted.
/ t ,.
,
SPECIFICATION
Title of the invention
Disc-Shaped Recording Medium
Background of the Invention
Field of the Invention
This invention relates to an disc-shape recording medium.
More particularly, it relates to a disc-shaped recording medium
on which compressed audio PCM data are recorded and which may be
advantageously employed in a small-sized portable disc
recording/reproducing apparatus.
Summary of the Invention
The present invention provides a disc-shaped recording
medium in which compressed audio data are recorded by optical
means, wherein, with the inner diameter of a data recording
region of a disc being set t o a predetermined value within a
range of 28 to 50 mm, the outer diameter of the data recording
region for inner diameter of said data recording region of 28mm
is set in a range from 58 to 62 mm and said outer diameter for
said inner diameter of 50 rnm is set in a range from 71 to 73 mm,
whereby -the recording medium may be used with a small-sized
portable disc recording/reproducing apparatus and a playback time
about as long as that of a standard 12 cm CD may be realized by
recording compressed audio data having the compression rate of
e.g. 1/4,
Description of Related Art
1
An optical disc may have a recording capacity larger by two
or three digits than that of a magnetic disc, while enabling
accessing at a higher speed than that for a tape recording
medium. The optical disc also has an advantage that it enables
contactless data recording/reproduction on or from the medium,
and is superior in durability, and hence has become more popular
in recent years. A so-called compact disc (CD) is among the
widely known types of the optical discs.
Meanwhile, for providing a port able and, above all, a
pocketable headphone stereo or similar recording/reproducing
apparatus, with the use of the optical disc, a compact disc with
a disc diameter o-P 12 cm and a compact disc with a disc diameter
of 8 cm (so-called CD single) have been prescribed, as long as
the disc format is, concerned. However, with the disc diameter
of 12 cm, the recording/reproducing apparatus becomes 'too bulky
to be portable. Therefore, a disc 8 cm or less in diameter may
be thought to be convenient. However, if it is attempted to
construct a portable or pocket size recording and/or reproducing
apparatus with the use of an optical disc 8 cm or less in
diameter, the following problem is raised.
In the case of a standard CD format, in which an optical
disc; on which are recorded stereophonic digital rCM audio
signals sampled with a sampling frequency of 44.1 kHz and
quantized by 16 bits, is supplied by a producer, and in which
these signals are exclusively reproduced by the user (CD-DA
a L
format), the playback time (recording time) of the disc which is
8 cm in diameter is 20 to 22 minutes at most, meaning that a
symphony of classical music can not be recorded completely on one
disc side. The playback time of 74 minutes or longer, which is
approximately equal to that of the compact disc 12 cm in
diameter, is desired. Moreover, with this CD-DA format,
recording by the user is not feasible. In addition, a
contactless type optical pickup device is vulnerable to
mechanical vibrations and subject to detracking or defocusing.
Thus, when 'the apparatus is to be portable, some strong measures
need to be taken to prevent adverse effects of detracking or
defocusing on the reproducing operation.
With the CD-I (CD-interactive) format, the levels A to C as
shown in the following Table 1 are prescribed as a modes for
recording/reproducing bit-compressed digital audio signals.
Table 1
levels sampling number bandwidth playback time
of
frequency bits for (stereo/
quantiza- monaural)
tion
A 37.8 kHz 8 17 kHz 2/4
B 37.8 kHz 4 17 kHz 4/8
C 18.9 kHz 4 8.5 kHz 8/16
When reproducing a disc recorded with, for example, the
level B mode, signals obtained by fourfold bit compression of
standard CD-DA format digital signals are reproduced. Thus, if
3
~~~~'~~'~
all of the recorded data are stereophonic audio compressed data,
playback time becomes fourfold, or reproduction of eight-channel
data, becomes possible, so that reproduction for 70 minutes or
longer becomes possible with an optical disc of the order of 6
cm in diameter.
Meanwhile, with the CD-I format, the disc is rotationally
driven at the same linear velocity as that -Por the standard CD-DA
format, so that the continuous audio compressed data are
reproduced at a rate of one unit to n reproducing units on the
disc, where n is a figure corresponding to the playback time or
the bit compression rate of data and is equal to 4 (n=4) with the
level B stereo mode. This unit is termed a block or sector which
is made up of 98 frames and has a period of 1/75 second.
Therefore, with this level B stereo mode, a data string in which
one of four sectors is an audio sector, such as
S D D D S D D D ...
whe re S i s an and i o secto r and D i s othe r data secto r or secto rs ,
is recorded on the sector-by-sector basis on the disc. However,
for actual recording, since the above data string undergoes a
predetermined encoding similar to that -far ordinary CD format
audio data, such as error correction coding and interleaving,
data of the audio sector S and data of the data sector D are
arranged in a scrambled fashion in the recording sectors on the
disc. The other data sectors D may for example be video or
computer data. When the bit-compressed audio signals are also
4
i~~~~~~~
used for the data sector D, a data string in which four-channel
audio sectors S1 to S4 are cyclically arranged, that is a data
string
S1 S2 S3 S4 S1 S2 S3 S4 .....
is encoded and recorded on the disc. When recording and
reproducing continuous audio signals, channel 1 data
corresponding to the audio sector S1 are reproduced from the
innermost to the outermost sides of the disc. Channel 2 data
corresponding to the audio sector 52 are then reproduced from the
innermost to the outermost sides of the disc. Subsequently,
channel 3 data corresponding to the next audio sector S3 are
reproduced from the innermost to the outermost sides of the disc.
Finally, channel 4 data corresponding to the audio sector S4 are
reproduced from the innermost to the outermost sides of the disc
to enable data reproduction for a continuous fourfold time
duration.
However, for the above mentioned continuous reproduction,
several track jump operations for a longer distance spanking the
inner and outer disc peripheries are necessitated. Since the
track jump can not be achieved instantaneously, playback data
become depleted for a short time period, meaning that the
playback sound is momentarily interrupted. On the other hand,
when continuous audio signals are to be recorded, it is not
possible to record only the sector S2 signals, as an example,
because the data need to undergo interleaving at the time of
recording. That is, sector S2 data need to be interleaved with
adjoining and even near-by sectors, such as sectors S1 and S3,
such that it becomes necessary to rewrite signals of previously
recorded sectors. Thus it is extremely difficult to record the
continuous compressed audio data, while real-time processing is
virtually impossible.
IF these drawbacks could be eliminated, a
recording/reproducing time almost as long as or even longer than
that of a standard 12 cm CD could be realized with an 8 cm disc
or a disc of a lesser outer diameter. In such case, the sizes
of various disc parts need to be selected to optimum values by
taking account o-P the demand -for size reduction of the disc
recording/reproducing apparatus and a recording capacity of the
disc. Such selection of the sizes of the various disc parts is
critical because it affects not only the size of the disc
recording/reproducing apparatus bu also the use feel and the
possibility of coming into widespread use of the apparatus.
Ob.iects and Summary of the Invention
In view of the above described status of the art, it is a
principal-object of the present invention to provide a disc-
shaped recording medium oh which compressed audio data are or the
like are recorded, whereby a moderate recording/repro~iucing time
may be assured as a disc-shaped recording medium having
compressed audio data or the like recorded thereon and with which
the disc size may be such as v o meet the demand for size
6
i w~~~'e7~'~
reduction of the recording/reproducing apparatus.
With the disc-shaped recording medium according to the
present invention, the inner diameter of the data recording
region of the disc is set so as to be within a range of 28 to 50
mm, and the outer diameters of the data recording region for said
inner diameter of 28 mm and 50 mm are set so as to be in a range
of 58 to 62 mm and in a range of 71 to 73 mm, respectively.
By setting the inner and outer diameters of the disc
recording region in this manner, a recording/reproducing time of
about 60 minutes at the minimum and about 72 to 76 minutes on an
average may be achieved by recording compressed audio data with
the compression rate of 1/4 at a track pitch of 1.6 um and a
linear velocity of 1.2 to 1.4 m/s.
Turning to the above conditions more specifically, if, with
the use of a disk of the same shape of the compact disc, the
inner diameter of the disc recording region is less than 32 mm,
the optical head travelling radially inwardly thrusts on a disc
driving spindle, because the lead-in region has an inner diameter
still less than the inner diameter of the disc recording region.
The opi;i cal head i s rest ri cted i n the manne r i n i is movement and
becomes unable to trace the lead-in region. In the case of a
disc which can be chucked or clamped positively with a shorter
width; such as a disc in which a protuberance is formed around
a centering hole on one major surface of the disc base plate,
it is possible to reduce the width of chucking or clamping
7
0~~~:9~~'~
further, so that the optical head may be moved further towards
the inner side of the disc and hence the inner diameter of the
data recording region may be reduced to 28 mm. Turning again to
the above conditions, if the data recording region is larger than
73 mm, the recording region is approximately of the same size as
the ordinary 8 cm CD and hence the demand for size reduction of
the disc recording/reproducing apparatus cannot be met
sufficiently.
Brief Description of the Drawings
Fig. l is a graph showing the relation between the inner
diameter and the outer diameter of a data recording region of a
disc-shaped recording medium embodying 'the present invention.
Fig. 2 is a plan view showing a disc-shaped recording
medium.
Fig. 3 shows a schematic plan view showing the disc-shaped
recordihg-medium accommodate in a cartridge.
Fig. 4 shows a sectional plan view showing the disc which
is loaded on the disc table of the disc driving unit.
Fig. 5 is a block diagram showing a disc
recording/reproducing'apparatus embodying the present invention.
Fig. 6 shows a format of a cluster structure constituting
a recording unit.
Fig. 7 shows a typical data structure of a sector or block.
Fig. 8 shows the contents of a sub-header.
Fig. 9 shows an in-sector data structure of a so-called CD-I
8
format.
Fig, 10 shows a format of a frame and a block or sector in
-the CD-standard.
Fig. 11 shows a data Format employed in the above described
disc recording/reproducing apparatus.
Fig. 12 shows the status of a controlled memory o-F a
recording system of the disc recording/reproducing apparatus
shown in Fig. 4.
Fig. 13 shows the status of a controlled memory of a
reproducing system of the disc recording/reproducing apparatus
shown in Fig. 4.
Embodiment
An embodiment of the disc-shaped recording medium according
to the present invention will be explained by referring to Fig.
1 to 3 . Fi g . 1 shows an i nne r d i amete r arrd an oute r di amete r of
a data recording region of a disc-shaped recording medium
embodying the present invention. Fig. 2 is a plan view of the
disc-shaped recording medium and Fig. 3. is a schematic plan view
showing the recording medium accommodated in a cartridge or
caddy.
Referring to Fig. 2, the disc-shaped recording medium, such
as a magneto-optical disk, has a central hole of a diameter dH,
or a centering hole 38, into which a spindle, not shown, is
introduced and chucked for rotationally driving a disc 32. The
disc 32 is inserted into a cartridge or disc caddy 31 shown in
9
i~~~~~~~
Fig. 3 to constitute a disc apparatus 30. A shutter plate 39 or
the like is movably mounted on the cartridge 31.
Turning again to Fig. 2, the disc 32 has a data recording
region RA having an inner diameter dI and an outer diameter dp.
A lead-in region or table of contents (TOC) region is provided
inwardly of 'the data recording region RA which has an inner
diameter d~. A region defined between the data recording region
RA and an outer disc diameter dp is a so-called rim region. An
optical head OP shown by a broken line in Fig. 2 is shown tracing
an innermost track of the lead-in region (with an 'inner diameter
d~) ,
Turning to a graph of Fig. 1, the outer diameter d~ and the
inner diameter dj of the data recording region RA are plotted on
the abscissa and the ordinate, respectively. Five curves L60,
L64, L68, LIZ, and L~6, in the figure represent the relation between
the outer diameter d~ and the inner diameter dI which will give
the recording/reproducing time duration for the CD-I format level
B stereo mode. The other conditiohs of the recording format of
the disc are similar to those of -the standard CD format (CD-DA
format) and include, for example, a 'track pitch of 1.6 pm and a
liner velocity of 1.2 m/s.
Although the lower limit for the inner diameter dI of the
data recording region RA is preferably 28 mm, the lower lim it is
preferably 32 mm for a disk flat on both sides, similarly to the
usual compact disk, in consideration of the width necessary for
to
disk chucking and clamping and the minimum size of -the optical
head that may be achieved under the present status of the art.
With the inner diameter dI of 32 mm, the inner diameter d~ of the
lead-in region is of an order of 30 mm. Since the diameter dH of
the centering hole 38 of 10 mm at most is required, a space as
small as about 10 mm may be conserved on one side of the
centering hole 38 between the centering hole 38 and the inner
periphery of the lead-in region. Since an allowance for
chucking and clamping is required in the proximity of the
centering hole 38, the size of the optical head between the
center and its outer wall is limited to 10 rnm less the above
mentioned width for chucking and clamping, which is close to the
minimum size of the optical head that may be realized at the
present time. In light of the foregoing, it is necessary to set
the lower limit of the inner diameter d~ of the lead-in region
and the lower limit of the inner diamete r dI of the data
recording region RA to about 30 mm and 32 mm, respectively.
The upper limit of the inner diameter dI of the data
recording region RA is set so as to be equal to the equal to the
inner diameter of the standard CD data recording region, or 50
mm, in consideration that a size in excess of the standard CD
size gives rise to no particular merit but results only in a
reduced recording capacity.
Thus it is preferred that the inner diameter dI of the data
recording region RA be selected within a range of 32 mm to 50 mm.
lx
The outer diameter dp of the data recording region RA may be
determined in dependence upon the inner diameter dI by taking
account of the required value of the recording capacity. Under
the present data compression technology, the data compression
rate which will satisfy the necessary sound quality, for example,
the sound quality of an FM broadcast level, is about 1/4 or
fourfold at most, such that, -For example, the above mentioned
level B stereo mode is most desirable. With the order condition
being the same as those for the standard CD, and with the linear
velocity being 1.2 m/s, the relation between the
recording/reproducing time and the inner and outer diameters of
the data recording region is as shown by the curve LS~ to L~6 in
Fig. 1. On the other hand, an index of a recording/reproducing
time most desirable to the user is the recording time for a
symphony of classical music, that is, a recording/reproducing
time of 74 minutes at the maximum, which is almost equal to that
of the currently available 12 cm CD. It will be noted that the
diameters d~ to dI for which the recording/reproducing time of 72
to 76 minutes at the minimum may be assured are encompassed by
a cross-hatched region in Fig. 1. If an increase or decrease in
the data recording capacity, due to changes in the recording
conditions or the like is taken into account, it is preferred to
set the outer diameter d0 of the data recording region RA so.as
t o be in a range from 60 to 62 mm (a range between points Pa and
Pb in Fig. 1) and in a range 'From 71 to 73 mm ( a range between
12
points P~ to and Pd in Fig. 1 ) for the inner diameters dI of the
data recording region RA o-F 32 mm and 50 mm, respectively
As a particular example, one of most desirable values is
(the inner diameter di of 'the region RA) = 32 mm; and
(the outer diameter d~ of the region RA) = 61 mm
as shown at Q~ in Fig. 1. As other sizes, for example,
(inner diameter d of the centering hole df~) = 10 mm;
(inner diameter of the Lead-in region d~) = 30 mm; and
(outer diameter dp of the disc) = 64 mm.
If the disc is accommodated in a cartridge or caddy 70 mm
x 74 mm in size and presented in this state to the market,
recording and/or reproduction on or from the disc becomes
possible with an ultra-small pocket size recording/reproducing
apparatus.
As another example of the size,
(inner diameter di of the data recording region RA) = 42 mm;
and
(outer diameter d~ of the data recording region RA) = 67 mm
as shown at point Q2 in Fig. 1, are also desirable, for which
other sizes may be selected so that
(inner diameter of the Lead-in region d~) = 40 mm; and
(outer disc diameter dp) = 70 mm.
Alternatively, the diameters di and d~ may be selected so
that
(inner diameter dI of data recording region RA) = 50 mm; and
13
(outer diameter d~ of data recording region RA) = 72 mm
for which other sizes may be selected so that, for example,
(inner diameter of the lead in region d~) = 46 mm; and
(outer disc diameter dp) = 76 mm. ,
It is to be noted that a variety of combinations other than
those specified above are possible as long as the above mentioned
size conditions are satisfied.
The above conditions are those for a disk in the form of a
flat plate similar to a compact disc. However, if a disc
employed is of a structure in which chucking or clamping may be
achieved reliably with a shorter width, the inner diameter d1 of
the data recording region RA may be diminished to an order of 28
mm at the minimum. A typical example o-f the arrangement is a
recording disk arranged as shown in Fig.4. This example is
explained by referring to Fig.4.
Referring to Fig.4, the disk-shaped recording medium is a
magneto-optical disk 100, and a magnetic metal plate placed on
one major surface of the disc is attracted by a magnet 205 placed
on the disc table 205 for clamping the magneto-optical disc 100
onto the disctable 201.
Referring to Fig.4, the magneto-optical disc 100 employed
in the disk loading system taking advantage of the attractive
force of the magnet includes a disk base plate 101 molded from
a transparent synthetic resin, such as polycarbonate resin, into
the shape of a disk. An information signal recording layer for
14
~~~'~~'~
recording information signals is deposited on one major surface
101a of the disk base plate 101a. The other surface 101b of the
disk base plate 101 opposite to the surface 101a of the disk base
plate '101 of the magneto-optical disk 101 carrying the
information signal recording layer is an information signal
write-read surface and a light beam is irradiated on the signal
recording layer from the write-read surface side for recording
and/or reproducing the information signa'Is.
The disc base plate 101 has a centering hole 102 engaged by
a centering member 202 adapted for bringing the center of
rotation of the magneto-optical disc 100 into coincidence with
the axis of rotation of the disk table 201 when the disc is
loaded on the disc table 201 of 'the disc driving unit 200. The
magnetic metal plate 103 in the form of a flat disc is affixed
to a mid portion of the major surface 101a of the disc base plate
101 for closing the centering hole 102 such as with an adhesive.
If the disc base plate 101 of the magneto-optical disc 100
has a thinner thickness of an order of l,2 mm, the centering
hope 102 engaged by the centering rnember 202 provided on the disc
table 201 cannot be of a sufficient depth. In addition, since
the metal plate 103 is provided on the major surface 101a of the
disc base plate 100 for closing the centering hole, the centering
member 202 engaging in the centering hole 102 cannot be of a
sufficient-height.
The centering member 202 operating 'For bringing the center
1s
~~9'"d~'~
of rotation of the magneto-optical disc 100 into coincidence with
the axis of rotation of the disk table 201 on loading the
magneto-optical disc 100 onto the disk table 201 is mounted so
as to be reciprocated axially of the driving shaft 203 supporting
the disc table 201 and be biased by a coil spring 204 towards the
distal end of the driving shaft 203. When the magneto-optical
disc 100 is being loaded onto the disc table 201, the centering
member 202 is advanced axially of the driving shaft 203 under the
load of the magneto-optical disc 100 against the bias of the coil
sprig 204 into engagement with the centering hole 102 for
centering the magneto-optical disc 100 wit respect to the disc
table 201.
For assuring such centering operation, the centering member
202 is of a sufficient height for providing a larger stroke of
relative movement between the magneto-optical disc 100 and the
centering member 202. That is, the other major surface 101b of
'the disc base plate 101 opposite to the major surface 101a
provided with -the metal plate 103 is formed with an annular
projection 104 surrounding the centering hole 102 to provide for
a suff i c Tent depth of the cente r i ng hol a 102 and a suff i c i ent
height of the centering member 202 to assure positive centering.
Meanwhile, the magneto-optical disc 100, thus centered by
the cente ri ng member 202 and 1 oaded i n thi s state on the di sc
table 201, has the end face of the annular projection 104 as a
loading reference surface 104a, and is loaded on the disc table
16
i~~~~~~i'~
201 with the loading reference surface resting on a disc
receiving surface 201a of the disc table 201, When loaded on the
disc table 201, the magneto-optical disc 100 is clamped by the
metal plate 103 being attracted by a magnet 205 arranged on the
disk table 201 and is driven into rotation by a driving motor 206
in unison with the disc -table 201.
With 'the use of the above described disc-shaped recording
medium, since a narrower or smaller clamping width suffices for
clamping the disc, the inner diameter dI of the data recording
region may be diminished to an order of 28 mm. The fact that the
inner diameter dI of the data recording region may be located at
a more inner place of the disc is desirable in view -that a disc
area with satisfactory characteristics may be utilized
effectively. It is noted that, when molding a resin to form a
diskc, resin is injected at a mold portion facing an inner
portion of the disc. While it is extremely difficult to cure the
disk in its entirety after resin injection, and it is generally
the rim of the disk that is cured first and lowered in
characteristics, such as due to bifringence, warping or
deterioration in impurity concentration, the inner disk area
exhibits satisfactory characteristics, so that it is desirable
to utilize this inner disk area effectively. If, in view of
possible increase or decrease of the data recording capacity
caused by changes in the recording conditions or the like, the
inner diameter dI of the data recording region is set to 28 mm,
17
~'~~'t~~'i
it suffices to set the minimum value of the outer diameter d0 to
58 mm, as shown at point Pc in Fig. 1.
The following is an example of various sizes which are most
desirable when using the disc designed for the above described
clamping system.
In the first place, the diameter of the centering hole 102
is enlarged to, for example, 11 mm for enlarging an area of the
metal plate '103 facing the magnet 205 to assure positive
clamping. By selectihg the end face 104a of the projection 104
as the loading reference plane for positioning the disc in height
during disc loading, the range o-F travel of the optical head is
extended towards an inner region. The inner diameter of the data
recording region di is set to 31 mm. The outer diameter d0 of
-the data recording area at this time is 61 mm, as an example.
A point C~ in Fig.1 is a point satisfying the above conditions for
the inner diameter di and the outer diameter d0. A lead-in
region having a width of 1.5 mm is formed on the inner side of
the;data recording region having an inner diameter of 31 mm, and
lead-in data are recorded as prepits in the lead-in region. A
lead-out region having a width of 0.5 mm is formed on the outer
side of the data recording region having an outer diameter of 61
mm and lead-in data are recorded as prepiis in the lead-out
region:
The abov a described magnet clamping system may be used in
conjunction not only with the magneto-optical disk 100, but also
with various other discs, such as an optical disc having an
aluminum reflective surface similar to the conventional compact
disc.
The cross-hatched region in Fig. 1 represents a combination
of the diameter di and d~ which may be adopted when a
recording/reproducing time longer than the above mentioned
maximum time duration of 72 to 76 minutes is desired or when the
data compression rate is to the lowered to improve the sound
quality.
Referring to Fig.5, an example o-P the disc
recording/reproducing apparatus employing, the above described
disc-shaped recording medium is hereinafter explained.
Fig.5 shows a schematic arrangement of the disc
recording/reproducing apparatus employing the above described
disc-shaped recording medium embodying the present invention.
In the disc recording/reproducing apparatus, shown in Fig.
5, a magneto-optical disc 2 rotationally driven by a spindle
motor 1 is employed as a recording medium. While a laser light
is irradiated by an optical head 3 on the magneto-optical disc
2, a modulating magnetic field consistent with recording data is
applied by a magnetic head 4 to the magneto-optical disc 2 for
recording data along a recording -track of the disc 2, by ways of
a so-called magnetic field modulation recording. On the other
hand; the recording track of the magneto-optical disc 2 is traced
with a laser light by the optical head 3 for photomagnetically
19
~~°4~'~~i'~
reproducing the recorded data,
The optical head 3 is constituted by a laser light source,
such as a laser diode, optical components, such as a collimator
lens, an object lens, a polarization beam splitter or a
cylindrical lens, and a split photodetector, and is arranged for'
facing the magnetic head 4 with the magneto-optical disc 2 in-
between. For recording data on the magneto-optical disc 2, the
optical head 3 irradiates a laser light tin a target track on the
magneto-optical disc 2 for recording data by thermomagnetic
recording. The modulating magnetic field consistent with the
recording data is applied to the target track by the magnetic
head 4 which is driven by a head driving circuit 16 of the
recording system which will be explained subsequently. The
optical head 3 detects a laser light irradiated on and reflected
by the target track for detecting the focusing error by a so-
called astigmatic method as well as detecting the tracking error
by a so-called push-pull method. When reproducing data from the
magneto-optical disc 2, the optical head 3 detects the difference
of a polarization angle (Kerr rotation angle) of the reflected
laser light from the target track to produce playback signals.
The output of the optical head 3 is supplied to an RF
circuit 5. The RF circuit 5 extracts the focusing error signal
and the tracking error signal from the output of the optical head
3 and transmits -the extracted signals to a servo control circuit
6 while converting the reproduced signals into corresponding
e~,'~~~'d~~~
binary signals and supplying the binary signals to a decoder 2.1
of the reproducing system, which will be explained subsequently.
The servo control circuit 6 is constituted by a focusing
servo circuit, a tracking servo circuit, a spindle motor servo
control ci rcuit and a thread servo control ci rcuit. The focusing
servo control circuit executes focusing control of an optical
system of the optical head 3 so that the focusing error signal
will be reduced to zero. The tracking servo control circuit
executes tracking control of the optical system of the optical
head 3 so that the tracking error signal will be reduced to zero.
The spihdle motor servo control circuit controls the spindle
motor 1 for rotationally driving the magneto-optical disc 2 at
a predetermined rotational velocity, such as at a constant linear
velocity. The 'thread servo control circuit causes the optical
head 3 and the magnetic head 4 to be moved to a target track
position on the magneto-optical disc 2 designated by the system
controller 7. The servo control circuit 6, which performs these
various control operations, transmits an information indicating
operating states of components controlled by the servo control
circuit 6 to the system controller 7.
Although the present disc recording/reproducing apparatus
has been described with reference to recording and reproduction
of the B-level stereo mode ADPCM audio data; the present
invention may also be applied to recordingand/or reproduction
of other mode ADPCM audio data in other CD-I system.
21
With the above described disc-shaped recording medium
according to 'the present invention, the inner diameter of the
data recording region is set to 32 to 50 mm, the outer diameter
of the data recording region for the inner diarneters of 32 mm is
set t o 60 to 62 mm and 'the outer diameter of the data recording
region for the inner diameter of 50 mm is set to 71 to 73 mm, so
that the recording medium may be used with a small-sized portable
disc recording/reproducing apparatus, while the compressed audio
data with the compression ratio of 1/4 are recorded on the
recording medium to realize a playback time about as long as that
of a standard 12 cm CD. That is, when recording compression
audio data with the compression ratio of 1/4, a track pitch of
1.6 um and a liner velocity of 1,2 to 1.4 m/s, the
recording/reproducing time may amount to about 60 minutes at the
minimum and about 72 to 76 minutes the average.
To the system controller 7 are connected a key input
operating section 8 and a display section 9. This system
controller 7 controls the recording system and the reproducing
system with the operating mode designated by an operating input
information from the key input operating section 8. The system
controller 7 supervises, on the basis of a sector-by-sector
address information reproduced from the recording track of the
magneto-optical disc 2 by the header time or sub-~ data, the
recording position as well as the reproducing position on the
recording track traced by the optical head 3 and the magnetic
22
head 4. The system controller 7 causes a bit compression mode
to be displayed on a display section 9 on the basis of bit
compression mode data in the reproduced data obtained from the
RF circuit 5 by means of a reproducing system as later described,
or of bit compression mode data in the ADPCM encoder 13
switchingly selected by the key input operating section 8. The
system controller also causes the playback time to be displayed
on the display section 9 on the basis of a data compression ratio
and the reproducing position data on the recording track in the
'. bit compression mode.
For displaying the playback time, the sector-by-sector
address information (absolute time information), reproduced from
the recording track of the magneto-optical disc 2 with the head
time or sub-Q data, is multiplied by a reciprocal of the data
compression ratio in the bit compression mode (four in case of
1/4 compression) to find an actual time information for display
on the display section 9. It is noted that, if an absolute time
information has been recorded (preformatted) on a recording track
of a magneto-optical disc, the preformatted absolute time
informati,;on may be read during recording and multiplied by the
reciprocal of the data compression ratio for display of the
current position in the form of the actual recording time.
It is noted that the recording system of the disc
recording/reproducing apparatus is prodded with an A/D converter
l2 to which an analog audio signal AIN is supplied from an input
23
terminal 10 by way of a low-pass filter 1't.
The A/D converter 12 quantizes the audio signal AIN, The
digital audio data obtained at the A/D converter 12 is
transmitted to an adaptive differential pulse code modulating
encoder (ADPCM encoder) 13. The ADPCM encoder 13 processes the
prescribed transfer rate digital audio data quantized from the
audio signal AIN by the ADPCM encoder 13 by a data compressing
operation in conformity to the various modes in the CD-I system
shown in Table I, and has its operating mode designated by the
system controller 7. For example, in the B-level mode of Table
1, the digital audio data are processed into compressed data
(ADPCM audio data) having a sampling frequency of 37.8 kHz and
the number of bits per sample equal to 4, before being supplied
to a memory 14. The data transfer rate with the B-level stereo
mode is reduced to 18.75 sectors/second.
In the embodiment of Fig. 1, it is assumed that the sampling
frequency of -the A/D converter 12 is fixed at the sampling
frequency of the standard CD-DA format, or 44.1 kHz, and that,
in the ADPCM encoder 13, bit compression from 16 bits to 4 bits
is performed after conversion of the sampling rate in conformity
to the compression mode, for example, from 44.1 kHz to 37.8 kHz
for level B. Alternatively, the sampling frequency of the A/D
converter 12 itself may be switchingly controlled as a function
of the compression modes. In this case, the cut-off frequency
of the low-pass filter 11 is also switchingly controlled as a
24
a~~~~~~',~
function of the switchingly controlled sampling frequencies of
the A/D converter 12. That is, the sampling frequency of the A/D
converter 12 and the cut-off frequency of the low-pass filter 11
may be simultaneously controlled in dependence upon the
. compression modes.
The memory 14 is used as a buffer memory in which data
writing and readout are controlled by the system controller 7 and
which transiently stores ADPCM audio data supplied from the ADPCM
encoder 13 for continuous recording on the disc as the occasion
may demand. That is, in the B-level stereo mode, the compressed
audio data supplied from the ADPCM encoder 13 has its transfer
rate reduced to 18.75 sectors/second, these compressed data being
cohtinuously written 'in 'the memory 14. Although it suffices to
record the compressed data (ADPCM data) at a rate of every four
sectors, as explained hereinbefore, it is practically impossible
to record the data at this rate on the real time basis, and hence
the sectors are recorded continuously as later explained. Such
recording is performed in a burst fashion (discontinuously) at
a standard data transfer rate of 75 sectors/second, by taking
advantage of a quiescent period, with a cluster, composed of a
predetermined number o-F, e.g. 32 sectors, as a data recording
unit. That is, in the memory 14, the B-level stereo mode ADPCM
audio data, which has been cowtinuously written at the lower
transfer rate of 18.75'(=75/4) sectors/second conforming to the
data comp ress i on rat i o , i s read out as reco rd data i n a bu rst
fashion at the above mentioned transfer rate of 75
sectors/second. The overall data transfer rate of the data read
out and recorded in this way, inclusive of the non-recording
period, is a lower rate of 18.75 sectors/second. However, an
instantaneous data transfer rate within the time of the burst-
like recording operation is equal to the above mentioned standard
rate of 75 sectors/second. Therefore, if the rotational velocity
of the disc is the same as that of the standard CD-DA format,
that is, a constant linear velocity, recording is made at the
same recording density and with the same recording pattern as
those of the CD-DA format.
The ADPCM audio data read out from memory 14 in a burst
fashion at the transfer rate of 75 sectors/second, that is, the
record data, is supplied to an encoder 15. With a data string
supplied from memory 14 to encoder l5, a data unit continuously
recorded with each recording is cornposed of a plurality of, e.g.
32 sectors, and a few cluster-linking sectors arrayed before and
after the cluster. The cluster-linking sector has a length
longer than the interleaving length at the encoder 15, so that,
even when the sector undergoes interleaving, data of other
clusters remain unaffected. Details of the recording on the
cluster-by-cluster basis will be discussed later by referring to
Fig: 5.
The encoder 15 processes the record data supplied in a burst
fashion from the memory 14 with an error correcting coding
26
.. operation, such as by parity addition or interleaving, or eight-
to-fourteen modulation (EFM). The, recording data, thus encoded
by the encoder 15, is supplied t o the magnetic head driving
circuit 16.
To the magnetic head driving circuit 16 is connected the
magnetic head 4 which drives the magnetic head 4 to apply a
modulating magnetic field conforming to the record data to the
magneto--optical disc 2.
On the other hand, the system controller 7 performs a
recording position controlling operation for the memory 14 and,
based. on the controlling operation, performs a disc recording
position control so that 'the above mentioned record data read out
in a burst fashion from memory 14 will be recorded continuously
on the recording track of the magneto-optical disc 2. For the
recording position control, the record position of the record
data read out in a burst fashion from the memory l4 is supervised
by the system controller 7, and control signals designating the
record position on the recording -track of the magneto-optical
disc 2 are supplied to the servo control circuit 6.
The ,reproducing system in the disc recording/reproducing
apparatus is hereinafter explained.
The reproducing system is adapted for reproducing the record
data continuously recorded by the above described recording
system on the recording track of the magneto-optical disc 2, and
is provided with a decoder 21, to which is supplied a playback
27
output, which has been generated by the optical head 3 tracing
the recording track on the magneto-optical disc 3 with a laser
light, and which has been converted into binary format signals
by the RF circuit 5.
The decoder 21 is associated with the encoder 15 in the
above described recording system, and processes the playback
output, converted into the binary -Format signals by the RF
circuit 5, with the above mentioned decoding for error correction
and EFM decoding, and reproduces the above mentioned B level
stereo mode ADPCM audio data at a transfer rate of 75
sectors/second which is faster than the normal transfer rate in
the above mentioned B level stereo mode. The reproduced data,
produced by the decoder 21, is supplied to a memory 22.
The memory 22 has its data writing and readout controlled
by the system controller 7 so that the playback data supplied
from decoder 21 at a transfer rate of 75 sectors/second is
written in a burst fashion at the transfer rate of 75
sectors/second. Also the playback data written in a burst
fashion at the transfer rate of 75 sectors/second in the memory
22 are continuously read out therefrom at the regular B-level
stereo mode of 18.75 sectors/second.
The system controller 7 also performs a memory control of
writing the reproduced data in the memory 22 at the transfer rate
of 75 sectors/second, continuously reading out the playback data
vFrom the memory 22 at the transfer rate of 18.75 sectors/second.
28
~~~~'~~'d
The system controller 7 performs, besides the above
mentioned memory control operation for memory 22, a reproducing
' position control from the recording track of the magneto-optical
disc 2, in such a manner that the playback data written in a
burst fashion by the above mentioned memory control in the memory
22 is reproduced continuously from the recording track of the
disc 2. The reproducing position control is performed by
supervising a reproducing position on the disc of the above
mentioned playback data written in a burst fashion in the memory
22 by system controller 7 and by supplying a control signal
designating the reproducing position on the recording track of
the magneto-optical disc 2 to the servo control circuit 6.
The B-level stereo mode ADPCM audio data, obtained as
playback data read out continuously from memory 22 at a transfer
rate of 18.75 sectors/second, are supplied to the ADPCM decoder
23.
l"his ADPCM decoder 23 is associated with the ADPCM encoder
13 of the recording system, and has its operating mode designated
by system controller 7. With the present disc
recording/reproducing apparatus, the B-level stereo mode ADPCM
audio data are expanded by a factor of four for reproducing the
digital audio data: The reproduced digital audio data is
transmitted by the ADPCM decoder 23 to a D/A converter 24.
The D/A converter 24 causes the digital audio data supplied
from the ADPCM decoder 23 to be converted into an analog audio
29
o~~~~~~~~
signal ApUT. The analog audio signal ApUT, obtained at the D/A
converter 24, is outputted via a low-pass filtor 25 at an output
terminal 26.
The reproducing system of the disc recording/reproducing
apparatus of the present embodiment is provided with a digital
outputting function so that the digital audio data at the output
of 'the ADPCM decoder 23 is outputted at a data output terminal
28 via a digital output encoder 27 as a digital audio signal DpUT
The recording/reproducing operation by the above described
disc recording/reproducing apparatus will be explained more
detail.
The record data, that is data read out from the memory 14,
is arranged into a cluster at an interval of a predetermined
number of, e.g. 32, sectors or blocks, and several cluster-
linking sectors are arrayed between adjoining clusters. In more
detail, referring to Fig. 6, each cluster Cn consists of 32
sectors or blocks BO to B31, and five linking sectors L1 to L5
are arranged between these clusters C~for linking the adjoining
clusters. For recording a cluster, such as a k'th cluster Ck,
the 32 sectors BO to B31 of the cluster Ck and the linking
clusters ahead and at the back of the cluster Ck, namely the
three sectors L3 to L5 towards the cluster Ck_1 (run-in blocks)
and the three blocks L1 to L3 towards the cluster Ck+1, making a
total of 38 sectors, are recorded as one unit. The 38-sector
record data are transmitted fram the memory 14 to the encoder 15
where interleaving is carried out for data rearrangement over a
distance of up to 108 frames corresponding to ca. 1.1 sector.
However, 'the data within the cluster Ck are safely contained
within a range of from the run-in blocks L3 to l_5 to the run-out
blocks L1 to L3 without affecting the remaining clusters Ck_~ or
Ck+1' Meanwhile, dummy data, such as 0, are arrayed in -the
linking sectors L1 to L5 to avoid adverse effects which
interleaving might have on the data per se. When recording the
next cluster Ck+1, three sectors L3 to L5 of the five linking
sectors L1 to L5 bet~raeen the current cluster and the next cluster
Ck+1 are used as the run-in blocks, so that the sector L3 is
recorded superfluously without causing any inconvenience. The
sector L3 of the run-in block or the sector L3 of the run-out
block may be omitted, so that recording may be performed with the
remaining 37 sectors as a unit.
By recording on the cluster-by-cluster basis, there is no
necessity of taking account of an interference with the adjoining
clusters by interleaving, so that data processing may be
simplified significantly. On the other hand, if the record data
shou'Id be unable to be recorded normally due to malfunctions,
such as defocusing, detracking, etc., re-recording may be made
on the cluster-by-cluster basis and, if the record data should
be unable to be reproduced effectively, re-reading may be made
on the cluster-by-cluster basis.
Meanwhile, each sector or block consists of 12 synchronizing
31
bits, 4 header bytes and 2336 bytes of data per se D0001 to
D2336, arrayed in this order, making a total of 2352 bytes. This
sector or block array is represented as a 'two-dimensional array,
as shown in Fig. 7, wherein the 12 synchronization bits consist
of the f i rst byte OOH, ten bytes FFI-I and the 1 ast byte OOH i n the
hexadecimal system (H is a hexadecimal number). The next 4-byte
header consists of address parts for minute, second and block,
each one byte, and a mode data byte. These mode data mainly
indicate a CD-ROM mode, while a sector structure shown in Figs.
6 or 7 corresponds to the mode 2 of the CD-ROM format. the CD-I
is a standard employing the mode 2 and the contents of the data
D0001 to D0008 are prescribed as shown ~in Fig. 8.
Fig. 9 shows forms 1 and 2 of the CD-I standard, in which
12 synchronizing bits and 4 header bytes are -the same as those
of the CD-ROM mode 2 shown in Figs. 6 and 7. The next 8
subheader bytes are prescribed as shown in Fig. 8 wherein data
D0001 and D0005 are file numbers, data D0002 and D0006 are
channel numbers, data D0003 and D0007 are subcode data and data
D0004 and D0008 are data type data. The data D0001 to D0004 and
data D0005 to D0008 are the same data written in duplicate. The
next 2328 bytes consist of 2048 user data bytes, four error-
detecting bytes, 172 P parity bytes and 104 Q parity bytes, for
from l of Fig. 9A. This form L is used for recording letter
da~ta~, binary data and high compression video data. The 2328
bytes for form 2 of Fig. 9B consist of 2324 user data bytes,
32
downstream of the sub-header data, and 'the remaining 4 reserve
data bytes. This form 2 is used for recording compressed audio
data or video data. Tn the case of the compressed audio data,
18 128-byte sound groups (2304 bytes) are arrayed in the 2324
user data bytes, with the remaining 20 bytes representing a
vacant space.
Meanwhile, when recording the above-described sector-based
data on a disc, a coding operation such as parity addition or
interleaving or EFM encoding is carried out by the encoder 15,
so -that recording is performed with a recording format shown in
Fig. 10.
Referring to Fig. 10, each block or sector consists of 98
frames of 1st to 98th frames, with each frame being 588 times a
channel clock period T(588T). Within each frame, there are a
frame synchronizing pattern part of 24T (plus 3T for linking),
a subcode part of 14T (pl us 3T for 1 i nki ng ) and data part of 544T
(for audio data and parity data). The 544 T data part consists
of 12 bytes or symbols of audio data, 4 bytes of parity data, 12
bytes of audio data and 4 bytes of parity data which have been
processed by EFM (eight-to-fourteen modulation). Audio data in
each frame is constituted by 24 bytes or 12 words because each
word of the audio sample data consis s of 16 bits. The subcode
part is the 8-bit subcode data which has undergone EFM and is
arrayed in a block with 98 frames as a unit, each bit
constituting one of eight subcode channels P to W. The subcode
33
parts of the first and second frames are block synch patterns S~
and S~ which violate the EFM rule, each of the subcode channel P
to W being constituted by 96 bits for the thi rd to 98 'the frames.
The above mentioned audio data, recorded after interleaving,
are deinterleaved during reproduction into audio data of a data
array conforming to the regular time sequence. The CD-I data,
such as are shown in Figs. 7 and 9, may be recorded in place of
the audio data.
Meanwhile, digital data obtained at the A/D converter 12 in
the disc recording/reproducing apparatus shown in Fig. 5, are
data similar to those of the CD-DA format, that is the audio PCM
data with the sampling frequency of 44.1 kHz, the number of
quantization bits equal to 16 and a data transfer rate of 75
sectors/second, as shown in Fig. 11. When the data is
transmitted to the ADPCM encoder 13 so as to be bit-compressed
to the above-mentioned stereo mode, the digital data are
conve rted i nto data wi th a sampl i ng f requehcy of 37 . 8 kHz and the
number of quantization bits is compressed to four bits. Thus the
output data are the ADPCM audio data having the data transfer
rate reduced by 1/4, or to 18.75 sectors/second. The B level
stereo mode ADPCM audio data, continuously outputted at a
trans-Fer rate of 18.75 sectors/second from the ADPCM encoder 13,
are supplied to the memory 14.
Referring to Fig: 12, the system controller 7 controls the
memory 14 in such a manner that a write pointer W of the memory
~~~°~.p'~fi"'~
14 is continuously incremented at a transfer rate of 18.75
sectors/second to continuously write the ADPCM audio data in the
memory 14 at a transfer rate of 18.75 sectors/second and, when
the data volume of the ADPCM audio data stored in the memory 14
exceeds a predetermined volume K, a read pointer R of the memory
14 is incremented in a burst fashion at the trans-Fer rate of 75
sectors/second to read out a predetermined volume K of the ADPCM
data in a burst fashion from the memory 14 as, record data at the
above mentioned transfer rate of 75 sectors/second. It is noted
that the above predetermined volume K has one-cluster data as a
unit.
That is, in the recording system of the disc
recording/reproducing apparatus shown in Fig. 5, the ADPCM audio
data continuously outputted at the transfer rate of e.g. 18,75
sectors per second from the ADPCM encoder 13 are written in the
memory 14 at the above mentioned transfe r rate of 18.75
sectors/second. When the data volume of the ADPCM data stored
in the memory 14 exceeds the predetermined data volume K, the
data vol ume K of -the ADPCM and i o data i s read out i n a bu rst
fashion from memory 14 at the transfer rate of 75 sectors/second
as record data, so that input data can be continuously written
in the memory 14 while a data write region in excess of a
predetermined volume is perpetually maintained within 'the memory
14. By recording the recording positions on the recording track
of the magneto-optical disc 2 under control by the system
controller 7, -the record data read out in a burst 'Fashion from
the memory 14 can be recorded consecutively on the recording
track on the magneto-optical disc 2. Since a data vacant region
in excess of a predetermined volume is maintained in the memory
14, data can be continuously written in the data-depleted region
in excess of the predetermined volume even if the system
controller 7 detects that a track jump etc. has occurred due to
disturbances or the like to discontinue a recording operation on
the magneto-optical disc 2, and the resetting operation may be
carri ed out i n the i nterim. Thus, i nput data can be conti nuousl y
recorded without dropout on the recording track of the magneto-
optical disc 2.
Meanwhile, header time data corresponding to the physical
address of the sectors are annexed to the ADPCM audio data on the
sector-by-sector basis, and recorded on the sector-by-sector
basis on the magneto-optical disc 2. Table of contents data
indicating the record region and the recording mode are recorded
i n a tabl e-of-contents regi on.
In the reproducing system of the disc recording/reproducing
apparatus shown in Fig. 5, the system controller 7 controls the
memory 22 in such a manner that, as shown in Fig. 13, the write
pointer W of the memory 22 is incremented at a transfer rate of
75 sectors/second to write the reproduced data in the memory 22
a~t the transfer rate of 75 sectors/second, the read pointer R of
the memory 22 is continuously incremented at a transfer rate of
36
~~~'~~ a~
18.75 sectors/second to continuously read out -the playback data
from memory 22 at the transfer rate of 18,75 sectors/second, and
the write pointer W of the memory 22 is intermittently
incremented at the 'transfer rate of 75 sectors/second in a burst
fashion, so that, when the write pointer W catches up with the
read pointer R, writing is discontinued. When the data volume
of the playback data stored in the memory 22 is lower than -the
predetermined volume L, writing is started again.
Thus, with the above described reproducing system of the
disc recording/reproducing apparatus, the system controller 7
controls the memory 22 in such a manner that the B-level stereo
mode ADPCM audio data reproduced from the recording track of the
magneto-optical disc 2 is written in a burst fashion in the
memory 22 at a transfer rate of 75 sectors/second, and read out
continuously from the memory 22 as playback data at the transfer
rate of 18,75 sectors/second, so that the playback data may be
continuously read out from the memory 22 while the data vacant
regi on i h excess of the p redete rmined vol ume L i s pe rpetual l y
maintained within memory 22. Also the playback data
i hte rmi tten-tl y read out f rom the magneto-opt i cal d i sc 2 may be
continuously reproduced from the recording track on the magneto-
optical disc 2 by controlling the reproducing position on the
recordihg track of the magneto-optical disc 2 by the system
controller 7. In addition, the data ;ead-out region in excess
of the predetermined volume L is perpetually maintained in 'the
37
memory 22, as described previously, so that, even when the system
controller 7 should de'tec't the occurrence of a track jump etc.
due to, for example, disturbances, and 'the operation of
reproducing the magneto-optical disc 2 is discontinued, the
playback data may be read out from the data readout region having
a space in excess of the predetermined data volume to continue
the outputting of the analog audio signals and the resetting
operation may be executed in the interim.
38
